This paper provides the authors' insights and discussions in four areas of yield optimization available to the mature semiconductor fabricator. The mature fab is arbitrarily defined as fabs older than 3 years having feature sizes of >0.5 /spl mu/m. The areas of yield optimization include: (1) cost and implementation considerations for an integrated data collection and information analysis system; (2) use of a quantified and partitioned D/sub 0/ yield model; (3) focus on baseline yield quantification and improvement practices versus excursion controls; (4) increased roles and responsibilities for yield improvement.